Rhombuniopsis songmeng Xiang, He & Zhang sp. nov.

Fig. 9A–F

Etymology: Derived from ‘Songmeng (ẇDz)’, the old name of present Songming County, where its type locality (Lake Babuhai) is located. The recommended Chinese name of this species is “ ẇDzmṉü ” (Pseudomonas aeruginosa).

Material examined. Holotype: Length 46.3 mm, from Lake Babuhai, Yanglin town (êūDz), Songming County, Kunming, Yunnan Province, China, 25.277047°N, 103.093158°E, 2021.6., collected by Hong Quan Xiang (KIZ1904601) (Fig. 10 A).

Paratypes: 10 specimens (KIZ1904602 – KIZ1904611): KIZ1904602–KIZ1904611, Lake Babuhai, Yanglin town, 25.277047°N, 103.093158°E, 2021.6., collected by Hong Quan Xiang.

Other-localities: Lake Lulianghai, Zhongshu Town (中NJDz), Luliang County, 25.01131°N, 103.66032°E, 2023.9.1. (KIZ1904612 – KIZ1904614), collected by Hong Quan Xiang.

Diagnosis. Shell ovate, periostracum dark brown to black, pseudocardinal tooth of the right valve with a thin groove at the top.

Description. Shell(Fig. 10A–F). Length 18–60 mm. Shell small, solid, of medium thickness, ovate, symmetrical; posterior margin ovate, ventral margin straight; the umbo with wavy wrinkles, often eroded; lateral teeth long; the left valve with two pseudocardinal teeth, divided to two opposite triangles by a slit, pseudocardinal tooth of the left valve with a thin groove at the top, connected to lateral teeth; ligament long; anterior adductor muscle scar deep, posterior adductor muscle scar relatively small. Periostracum shining black; nacre white, with non-obvious fine lines.

Comparison. This species can be differentiated from the most similar species R. tauriformis by having a relatively narrow shell, weak lines on the nacre, and a more backward umbo position.

Habitat and distribution: Extinct species that inhabited muddy to sandy substrates near tributary mouths of Lake Babuhai.